Typical processes for preparing polybenzimidazoles are described in Journal of Polymer Science, 50, 511 (1961), and in various United States patents.
U.S. Pat. No. 3,174,947 (U.S. Pat. No. Re. 26,065) describes a method of preparing high molecular weight aromatic polybenzimidazoles by melt polymerizing an aromatic tetraamine and a diphenyl ester or an anhydride of an aromatic dicarboxylic acid at an elevated temperature and thereafter further polymerizing the product of the melt polymerization in the solid state. According to this process, in order to produce polymers of sufficiently high molecular weight to be suitable for practical use it is necessary to pulverize the product of the melt polymerization prior to polymerization in the solid state and to conduct the solid state polymerization at an elevated temperature under a reduced pressure of less than 0.5 mm Hg or at an elevated temperature and in an inert gas stream over a prolonged period of time.
U.S. Pat. No. 3,313,783 describes a process which involves the solution polymerization of an inorganic acid salt of an aromatic tetraamine and a dicarboxylic acid or a derivative thereof with heat in polyphosphoric acid.
Another process for producing polybenzimidazoles is described in U.S. Pat. No. 3,509,108. In the process the monomers are initially reacted in a melt phase polymerization at a temperature above 200.degree. C. and a pressure above 50 psi. The reaction product is then heated in a solid state polymerization at a temperature above 300.degree. C. to yield the final aromatic polybenzimidazole product. The process requires that the initial reaction be conducted at a pressure above 50 psi (preferably, between 300-600 psi) in order to control the foaming encountered during the polymerization.
U.S. Pat. No. 3,555,389 describes a two-stage process for the production of aromatic polybenzimidazoles. The monomers are heated at a temperature above 170.degree. C. in a first stage melt polymerization zone until a foamed prepolymer is formed. The foamed prepolymer is cooled, pulverized, and introduced into a second stage polymerization zone where it is heated in the presence of phenol to yield a polybenzimidazole polymer product.
U.S. Pat. No. 3,433,772 describes a two stage polymerization process for the production of aromatic polybenzimidazoles which utilize an organic additive, such as an alkane having 11-18 carbon atoms or a polycarbocyclic hydrocarbon, in order to control foaming during the first stage.
Other United States patents relating to one-stage and two-stage production of polybenzimidazoles include U.S. Pat. Nos. 3,408,336; 3,549,603; 3,708,439; 4,154,919; and 4,312,976; all patents enumerated herein incorporated by reference.
Polybenzimidazole polymers are valuable for the production of high temperature stable molded and extruded products such as films and fibers.
Polybenzimidazole polymers are hydrophobic in nature. For this reason polybenzimidazole powders or shaped articles cannot be wet with a hydrophilic solvent. The hydrophobic character of polybenzimidazole polymers limits the utility of these resins for applications such as wet films and the like.
U.S. Pat. No. 3,578,644 describes the preparation of hydroxyl modified polybenzimidazoles by reacting a polybenzimidazole polymer with an omega-haloalkanol or a 1,2-alkylene oxide in the presence of a basic catalyst such as sodium hydride.
The polymers produced correspond to the formula: ##STR1## where R is a divalent aliphatic, alicyclic or aromatic group, and R.sup.1 is a divalent aliphatic group. The use of a haloalkanol reactant requires a basic catalyst, and an inorganic salt is formed as a byproduct. The use of a gaseous alkylene oxide reactant requires a pressure vessel for the reaction medium.
There is continuing interest in the development of new and improved processes for the modification of polybenzimidazole polymers.
Accordingly, it is an object of this invention to provide a process for modifying polybenzimidazole polymers.
It is another object of this invention to provide an improved process for increasing the hydrophilicity of polybenzimidazole polymers.
It is a further object of this invention to provide novel 2-hydroxyethylated polybenzimidazole polymers.
Other objects and advantages of the present invention shall become apparent from the accompanying description and disclosure.